The present invention relates to signal delaying circuitry and, in particular, to a high-speed time delay circuit that uses an externally applied signal to control with high precision the delay time of a digital signal.
To operate properly, high-speed integrated circuits often require precise timing of many signals to achieve coincident transitions between logic states. Transitions between logic states of high-speed signals occur at different times because of differences in signal path lengths and in signal propagation delay times of the integrated circuit elements.
One way of achieving the precise timing of a "late" signal and an "early" signal is to delay the "early" signal by an amount of sufficient duration that aligns the logic transitions of the signals. Such alignment can be accomplished by passing the "early" signal through a series of circuit elements that have fixed propagation delays. This expedient suffers from the disadvantage of requiring the use of redundant circuitry that occupies extra space on power. Moreover, the delay provided is of a fixed amount and is susceptible to propagation delay changes that result from temperature variations. The result is that a small propagation delay deviation is multiplied by the presence of the several delay-producing circuit elements in the series.